As wireless networks mature and become more widely used, higher data rates are offered. An example of such a wireless network is a wireless local area network (WLAN) using an 802.11, 802.11a, or 802.11b protocol generally referred to hereinafter as the 802.11 protocol. The 802.11 protocol specifies a 2.4 GHz (802.11b) carrier frequency for the traditional service and 5.2 GHz (802.11a) and 5.7 GHz (802.11g) carrier frequencies for newer, higher data rate services.
As with other radios, a wireless network adapter includes a transmitter and receiver connected to an antenna. The antenna is designed to provide maximum gain at a given frequency. For example, if a monopole antenna were designed to operate most effectively at 2.4 GHz, it would not optimally support operation at 5 GHz. Similarly, if a directive antenna were designed to operate most effectively at 5 GHz, backward compatibility with 2.4 GHz 802.11 would be compromised.